Android通过ViewPager实现左右滑动切换图片
想开发像人人网相册打开单张图片时候能左右滑动切换图片的效果,开始通过FlipperView实现,不能跟手拖动,效果不好,而且需要自己写很多代码来控制FlipperView中的View。后来发现Android 3.0之后的SDK中提供了android-support-v4包用以实现版本兼容,让老版本系统下的应用通过加入jar包实现扩展,得到新版的各种技术优势,例如Fragment等。
ViewPager是android-support-v4.jar包中的一个系统控件,继承自ViewGroup,专门用以实现左右滑动切换View的效果,使用时需要首先在Project->properties->Java Build Path->Libraries->Add External Jars中加入sdk目录下的extras/android/support/v4/android-support-v4.jar(如果找不到,则需要用sdk manager下载android support package)。加入这个jar包之后就可以使用ViewPager类了。
ViewPager的使用类似于ListView,需要有对应的Adapter进行数据绑定,实现图片切换仅需要继承PaperAdapter就可以了。继承后需要重写如下四个方法。- instantiateItem(ViewGroup, int)
- destroyItem(ViewGroup, int, Object)
- getCount()
- isViewFromObject(View, Object)
复制代码 类似于BaseAdapter,其中instantiateItem方法用来得到每个View,destroyItem用以控制当某个View不需要的时候的回收处理。isViewFromObject用来实现判断View和Object是否为同一个View。
Java代码- import java.io.FileNotFoundException;
- import java.util.List;
-
- import android.content.Context;
- import android.graphics.Bitmap;
- import android.net.Uri;
- import android.support.v4.view.PagerAdapter;
- import android.support.v4.view.ViewPager;
- import android.view.View;
- import android.view.ViewGroup;
- import android.widget.ImageView;
-
- public class TestAdapter extends PagerAdapter {
-
- private List<String> mPaths;
-
- private Context mContext;
-
- public TestAdapter(Context cx) {
- mContext = cx.getApplicationContext();
- }
-
- public void change(List<String> paths) {
- mPaths = paths;
- }
-
- @Override
- public int getCount() {
- // TODO Auto-generated method stub
- return mPaths.size();
- }
-
- @Override
- public boolean isViewFromObject(View view, Object obj) {
- // TODO Auto-generated method stub
- return view == (View) obj;
- }
-
- @Override
- public Object instantiateItem (ViewGroup container, int position) {
- ImageView iv = new ImageView(mContext);
- try {
- Bitmap bm = ImageFile.getBitmapSample(mContext, Uri.parse(mPaths.get(position)), 320, 480);//载入bitmap
- iv.setImageBitmap(bm);
- } catch (FileNotFoundException e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- } catch (OutOfMemoryError e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- }
- ((ViewPager)container).addView(iv, 0);
- return iv;
- }
-
- @Override
- public void destroyItem (ViewGroup container, int position, Object object) {
- container.removeView((View)object);
- }
- }
- import java.io.FileNotFoundException;
- import java.util.List;
- import android.content.Context;
- import android.graphics.Bitmap;
- import android.net.Uri;
- import android.support.v4.view.PagerAdapter;
- import android.support.v4.view.ViewPager;
- import android.view.View;
- import android.view.ViewGroup;
- import android.widget.ImageView;
- public class TestAdapter extends PagerAdapter {
- private List<String> mPaths;
-
- private Context mContext;
-
- public TestAdapter(Context cx) {
- mContext = cx.getApplicationContext();
- }
-
- public void change(List<String> paths) {
- mPaths = paths;
- }
-
- @Override
- public int getCount() {
- // TODO Auto-generated method stub
- return mPaths.size();
- }
- @Override
- public boolean isViewFromObject(View view, Object obj) {
- // TODO Auto-generated method stub
- return view == (View) obj;
- }
- @Override
- public Object instantiateItem (ViewGroup container, int position) {
- ImageView iv = new ImageView(mContext);
- try {
- Bitmap bm = ImageFile.getBitmapSample(mContext, Uri.parse(mPaths.get(position)), 320, 480);//载入bitmap
- iv.setImageBitmap(bm);
- } catch (FileNotFoundException e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- } catch (OutOfMemoryError e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- }
- ((ViewPager)container).addView(iv, 0);
- return iv;
- }
-
- @Override
- public void destroyItem (ViewGroup container, int position, Object object) {
- container.removeView((View)object);
- }
- }
复制代码 Xml代码- <android.support.v4.view.ViewPager
- android:id="@+id/pager"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent" />
- <android.support.v4.view.ViewPager
- android:id="@+id/pager"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent" />
复制代码 Activity:
Java代码- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- mViewPager = (ViewPager)findViewById(R.id.pager);
- mAdapter = new TestAdapter(this);
- mViewPager.setAdapter(mAdapter);
- mAdapter.change(getList());
- }
-
- private List<String> getList() {
- List<String> list = new ArrayList<String>();
- list.add("file:///sdcard/Sunset.jpg");
- list.add("file:///sdcard/Winter.jpg");
- list.add("file:///sdcard/Water lilies.jpg");
- list.add("file:///sdcard/Blue hills.jpg");
- return list;
- }
复制代码 |